Mesosphere
Temperatures in themesosphere decrease with altitude. Since there are very few gas
molecules in the mesosphere to absorb the Sun’s radiation, the heat source here is the
stratosphere below. The mesosphere is extremely cold, especially at its top, about -90oC
(-130oF).
The air in the mesosphere is extremely thin: 99.9% of the mass of the atmosphere is below
the mesosphere. As a result, air pressure is very low. Although the amount of oxygen relative
to other gases is the same as at sea level, there is very little gas and so very little oxygen.
A person traveling through the mesosphere would experience severe burns from ultraviolet
light since the ozone layer which provides UV protection is in the stratosphere below them.
And there would be almost no oxygen for breathing! Stranger yet, an unprotected traveler’s
blood would boil at normal body temperature because the pressure is so low.
Despite the thin air, the mesosphere has enough gas that meteors burn as they enter the
atmosphere (Figure15.6). The gas causes friction with the descending meteor, producing
its tail. Some people call them “shooting stars.” Above the mesosphere is themesopause.
Astronauts are the only people who travel through the mesopause.
Figure 15.6: Meteors burn up as they hit the mesosphere. ( 23 )